It is known in the products sector relating to the packaging of loose material that there exists the need to arrange the material inside bags, which must be filled with a given and defined quantity of material and then sealed. It is also known that, for this purpose, automatic bag filling machines have been developed, an example of the machines consisting of so-called forming and filling machines which are able to perform at high speed the cycle involving forming of the bag, filling of the bag and final sealing of the bag mouth. The machines comprise in particular a station for filling the bag with the material contained inside a hopper arranged in a position substantially coaxial with the bag itself and at a height greater than the height of the bag mouth.
FIGS. 1 and 2 show a form-fill-seal (FFS) machine (also indicated below as FRS) with a forming station F, a filling station R with fixed grippers for gripping the bag engaged with the product feeding mouth, which station is provided with rotating valves able to open and close, a station S for sealing the bag mouth, and a conveyor 115 for conveying out of the machine the filled and sealed bag. FIG. 2 shows in schematic form the working sequence performed by means for conveying the bag from one station to another with opening of the mouth, closing of the mouth after filling, and sealing of the mouth with release by the grippers.
Also known, however, are filling machines—also indicated below as RGS—in which the bag is pre-formed and stored in a feeder from which it is removed and directly conveyed to the filling station.
Also known, both in the case of these latter machines and in the case of FFS machines, is an opening sequence of the bag mouth performed in the filling station R by means of suction cups for gripping the opposite side portions of the bag mouth which are fixed in the direction of feeding of the bag and movable in the direction perpendicular to the latter and grippers which instead are fixed in the transverse direction orthogonal to the direction of feeding of the bag and movable only in the direction of feeding of the bag so as to accompany the reduction in the width dimension of the mouth of the bag, following opening thereof.
However, for both types of known machines, the opening and closing movement of the bag mouth by means of the supporting grippers and of the suction cups for gripping the side portions of the bag is fixed by a start-of-cycle set-up operation depending on the minimum width dimension of the bags, which can be processed and remains fixed for all the possible different sizes of the bags processed by the machine. Correspondingly, also opening of the bag-holder device valves which enter into the mouth of the latter, once it has been opened, adhering to and tensioning its side portions so as to prevent material from escaping during filling, remains in turn fixed, again depending on the width of the bag being processed.
This means that, when there is a variation in the dimensions of the bag and in particular in its width, it may not be possible in a technically speaking reasonable amount of time and with reasonable efforts to modify the discharge cross-section of the feeding mouth without a further set-up operation which requires stopping the machine, disassembling its parts and manually adjusting the various positions before being able to start/restart production.
In the technical sector of filling machines also known are other types of machines called bagging machines for pre-formed bags in which the filling station includes means for adjusting opening of the valves of the bag-holder device depending on the size of the bag being processed. These adjustment means substantially consist of a selector, the relative positions of which determine different positions for stopping the opening rotational movement of the valves.
These types of machines, however, also have drawbacks due to the fact that, on the one hand, they require different set-ups for normal bags and gusseted bags, set-ups requiring the installation of different mechanical elements for the two bag types at the start of the cycle and, on the other hand, opening of the bag-holder valves takes place in the direction transverse to feeding of the bag, with the result that opening of the valves must necessarily be adapted to the size of the smallest gusset, thereby reducing the filling rate with a consequent increase in the cycle time when the gusset size is very small, with a reduction in the efficiency of the machine, which is particularly disadvantageous for the larger size bags which instead would require a higher filling speed in order not to penalize the overall production efficiency. In addition, handling of the gusseted bags requires that the folds of the gusset be opened at the time of filling and then folded back up again by means of a particularly delicate procedure.
The known methods consequently result in possible high operational downtimes of the machine, a reduction in the production capacity with a consequent increase in the unit production cost, as well as the need for personnel who are specialized and trained in performing retooling of the filling station.
U.S. Pat. No. 3,830,266A discloses an apparatus for filling with loose material bags having a mouth extending in a direction of width.